Actuating device for a motor vehicle brake system

ABSTRACT

An actuating device for a vehicle brake system may include a first piston-cylinder unit, the at least one working space of which is to be connected to at least one wheel brake of the vehicle via at least one hydraulic line, an electromechanical drive device and an actuating device, in particular a brake pedal. Methods for operating a vehicle brake system including such an actuating device and for diagnosing various portions of a vehicle brake system (e.g., but not limited to, a feed valve or a travel simulator) are also presented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a divisional application of U.S. patent Ser. No.13/883,971, filed on May 7, 2013, which is a National Stage of PCTInternational Application No. PCT/EP2011/004476, filed on Sep. 6, 2011,and claims priority of German Patent Application No. 10 2010 050 133.6,filed on Nov. 3, 2010 and German Patent Application No. 10 2010 045617.9, filed on Sep. 17, 2010. The disclosures of the aforementionedapplications are incorporated herein by reference in their entirety.

FIELD OF ENDEAVOR

The present invention relates to an actuating device for a vehicle brakesystem, comprising a first piston-cylinder unit, the at least oneworking space of which is to be connected to at least one wheel brake ofthe vehicle via at least one hydraulic line, further comprising anelectromechanical drive device and an actuating device, in particular abrake pedal.

STATE OF THE ART

Brake systems of the brake-by-wire type use a travel simulator. Theseare so-called power-brake systems with pump and reservoir without anymechanical fallback solution, which are little used in passenger cars.

In systems, with a mechanical fallback solution the so-called EHB isknown, see Braking Handbook of 2004, p. 272-274, in which a travelsimulator is hydraulically operated by the main cylinder and anon-linear travel simulator spring acts on the piston. This connectioncan be isolated by means of a solenoid valve, in order that if thepressure supply is lost no pedal loss is taken into account by thevolume take-up of the travel simulator. If the pressure supply failsduring braking, however, system weakness is unavoidable and can lead toaccidents. The principle of this concept is described in DE102006056907. Here the solenoid valve is, if currentless, normally open,meaning that if the power fails a considerable pedal loss occurs throughthe take-up of the volume of the piston in the travel simulator.

Other solutions based on vacuum brake boosters are described in DE 102004 011622, the object of which is a secure activation of a travelsimulator. Here the travel simulator is mechanically operated, combinedwith the pedal interface and can be deactivated by means of a magnet, iffor example the brake booster fails. Here also a pedal travel lossresults. In the same application a travel simulator is described, whichis arranged in the front section in the axis of the brake booster. Herethe travel simulator is locked via a magnet if the brake booster isintact. If the brake booster fails this locking does not work, and thebrake pedal operates with less pedal loss on the tandem main cylinderfor pressure generation. There is also a disadvantage here that in theevent of failure of the brake booster during braking this pedal lossreoccurs. If the system is designed with a small free travel a, then thepedal tappet during ABS with a low coefficient of friction and smalltandem main cylinder stroke already strikes the connecting tappetbetween the brake booster and the tandem main cylinder, so that thetravel simulator effect is deactivated. This solution also involves along installation length, which from the crash point of view is adisadvantage since, for example, the engine presses on the tandem maincylinder with the brake booster thereby pushing the pedal back leadingto considerable foot injuries.

A further solution is described in DE 10 2008 063771. Here the travelsimulator is mechanically operated with an electromechanical travelsimulator arrest. This is deactivated if the brake booster or the powersupply fails. Then the fallback solution, in which the pedal tappetimpinges directly on the main cylinder, comes into play. Throughdecoupling the pedal tappet travel and the main cylinder piston travelvia the travel simulator it is known that smaller piston diameters canbe used, which in the event of brake booster failure results in smallerpedal forces. This solution is complicated and requires a longinstallation length.

A complaint about travel simulator systems is that when braking with thevehicle at a standstill the hard stop when the travel simulator actuatesis perceptible and irritates the driver. During braking to a standstillthis is not the case, since the foot force immediately follows thevehicle deceleration and the hard stop is only reached at full braking.

Systems with travel simulator are extremely safety-critical, since inthe event of failure of the brake booster the fallback solution mustoperate reliably. This means that all safety-related components andfunctions must be diagnosable. These include, for example, the mobilityof the travel simulator housing or pistons, and the functioning of theshutoff valves. In systems in which the push-rod piston during operationrequires the volume in the travel simulator piston, the problem arisesthat in the event of failure of the brake booster this volume is missingfrom the brake circuit with subsequent correspondingly long pedaltravels, which is irritating for the driver. This is particularlyapparent in the extreme case in ABS control with low μ and fullactuation of the travel simulator and subsequent positive μ jump withsimultaneous brake booster failure. Here two effects occur in the samemanner: considerable pedal travels and low distance of the push-rodpiston from the floating piston, since the volume for the travelsimulator has been taken from the push-rod piston circuit. In so doing,should the push-rod piston impinge on the floating piston no furtherpressure is built up in the push-rod piston circuit.

The specifications of the vehicle manufacturers call for very high pedalforces which are approximately 20 times higher than the pedal force forachieving the blocking pressure with high μ. With today's systems theABS/ESP function then deactivates, but the components such as maincylinder, seals, brake lines, and so on, must withstand pressures of upto 350 bar.

New vehicle designs call for short installation lengths, in particularbetween the bulkhead and the brake pedal linking.

OBJECT FOR THE INVENTION

The object for the invention is to provide an actuating device of theaforementioned type which in terms of installation length, reliabilityand pedal travel is an improvement on the known solutions.

Solution of the Object

The object may be solved according to the invention by various featuresrecited in the accompanying claims.

With the solution according to the invention, in which a furtherpiston-cylinder unit is used, in order to create an auxiliary piston,which is operated by the actuating device or by the pedal tappet andimpinges on the first piston-cylinder unit or the main cylinder, in asurprisingly effective manner an actuating device for a vehicle brakesystem is provided, having a short installation length and highreliability and which extensively avoids pedal travel losses.

Advantageous embodiments or configurations of the invention arecontained in various claims.

The further piston-cylinder unit or the auxiliary piston can inparticular be disposed coaxially to the first piston-cylinder unit ormain cylinder, but can also, especially due to space considerations, beoperated by a lever system and be disposed in an offset manner.

The auxiliary piston is movable over the entire pedal stroke anddisplaces its volume in the mechanical hydraulic travel simulator. Thisis connected with the reservoir via a current-controlled 2/2-waysolenoid valve. This solenoid valve receives a variable current as afunction of the pedal stroke.

If for example the travel simulator piston jams, then this solenoidvalve operates as a pressure relief valve, so that the auxiliary pistoncan move with increased foot force and if necessary impinges directly onthe main cylinder piston. If necessary the brake booster can also bedeactivated. This pressure relief function can be diagnosed via motorcurrent, e.g., the armature current, of an electromechanical drivedevice.

The auxiliary piston and the solenoid valve diagnostics can be performedby connecting the drive device, especially the spindle, via a couplingto the auxiliary piston. Then the spindle and auxiliary piston are movedacross the entire stroke and measured via the redundant pedal strokesensors. Here the solenoid valve is open. In a second test the solenoidvalve is closed, which cannot result in any movement of the auxiliarypiston, and in so doing in particular the magnetic coupling is separate.

In this process the redundant pedal stroke sensors can also be tested.The volume of the auxiliary piston can also be provided to the push-rodcircuit or other brake circuits in each case via a further 2/2-waysolenoid valve or feed valve. In order in the event of failure of thebrake booster keep the pedal forces low, small main cylinder pistondiameters are necessary, but which at low pressures are known to requirea lot of travel for the relatively flat shape of the pressure-volumecurve. For this, especially at low pressures, the volume of theauxiliary pistons is used as a support. The feed valve can similarly betested, in that the spindle moves the piston when the switching valvesare closed, so that in the wheel brake cylinders no pressure is builtup. When the feed valve is closed the pressure transducer measures anincrease in pressure in the push-rod piston circuit, and none when thesolenoid valve is open.

In DE 10 2009 0316728 similarly a differential piston via a 3/2 solenoidvalve supplies volume to the small push-rod piston cylinder. Thisdifferential piston has a fixed connection with the push-rod pistonhowever and is not isolated via a coupling. Furthermore, it is notdesigned for a travel simulator system.

In the critical case referred to of the failure of the brake booster atlow μ the auxiliary piston can likewise provide support, in that thevolume of the auxiliary piston and possibly also of the travel simulatoris supplied to the push-rod piston circuit with the correct meteringbeing controlled via the pressure transducer. This prevents excessivepedal travel.

If in the extreme case the drive should jam during pressure decrease,then via the open feed valve and pressure control valve volume can bereleased into the reservoir controlled via the pressure transducer. Bymeans of a further feed valve per brake circuit this can also be appliedfor further brake circuits.

The pressure control valve is set to a maximum pressure according to thefoot power in conventional systems, at which the ABS/ESP no longerfunctions. At very high foot powers when the maximum pressure isexceeded the auxiliary piston with the filled travel simulator moves onthe main cylinder piston. In so doing it meets a stop, in this way highpressures are generated in the auxiliary piston and in the brake circuitonly a pressure level which is necessary for the brake for fading. Thebrake system can thus be designed for lower pressures, saving cost andweight.

The auxiliary piston requires less installation space and is well-suitedto the linking and securing of the sensors in a sensor module,comprising all sensors such as pedal stroke and angle of rotation. Thesecan be mounted together with the connector plug or cable on a smallcircuit board.

According to the invention, therefore, a sensor module is also providedfor, which on the actuating device groups together sensors to be used ina single unit in a simple and advantageous manner.

In patent application DE 10 2010 045 617.9 an actuating device of theaforementioned type is already described, having a furtherpiston-cylinder unit, the piston of which can be actuated by means ofthe actuating device and which is connected via a connecting device witha piston of the first piston-cylinder unit. An integrated electromotivedrive is provided here to serve as a booster. Although compared to thestate of the art this solution has numerous considerable advantages, itis not possible or desirable in every application. Thus there are casesin which the booster, e.g. in the form of an electromotively operatedpump, is already present, so that in principle only a master cylinder isnecessary. This applies, for example, to electrohydraulic brake systems,as described in the “Braking Handbook”, 1^(st) Edition, Vieweg Verlag.

The invention therefore also provides an actuating device, whichimproves on the known solutions and which can advantageously be used onsystems with existing boosters, such as for example an EHB.

With this solution, in which the piston of the further piston-cylinderunit is actuated by the actuating device, in a surprisingly advantageousmanner an actuating device for a vehicle brake system, in particular amotor vehicle brake system, is provided which can be used in manydifferent ways, in particular in cases where a booster device is alreadyprovided or specified.

Thus the advantages of a further piston-cylinder unit (auxiliarypiston), which result especially from the fact that in the event of afailure of the brake boosting additional hydraulic volume can be fedinto the brake circuits, can be applied in many different ways. Furtheradvantages consist of smaller pedal travels and higher achievablepressure levels. In DE 10 2009 031 672 a brake system is indeed alreadydescribed, in which by means of an additional piston-cylinder-device(additional piston) additional hydraulic medium can be supplied in acompensation reservoir or in a brake circuit. In this system, however,the additional piston is operated by an, especially, electromagneticdrive.

Furthermore, by means of the pressure in the cylinder of the second orfirst piston-cylinder unit a travel simulator can be operated. Here thetravel simulator can be deactivated especially via a solenoid valve.

The further piston-cylinder-unit can advantageously be activated anddeactivated by means of a solenoid valve.

As illustrated in patent application DE 10 2010 045 617.9 there arevarious advantageous embodiments of the spatial disposition of thefurther piston-cylinder unit in relation to the tandem main cylinder.Reference is made for disclosure purposes to these statements, withwhich an adaptation of the various spatial conditions, for example alsoa reduction in the installation length, is easily possible.

The invention also further concerns a method for operation of anactuating device for a vehicle brake system, and advantageousconfigurations of this method. With this method in an advantageousmanner via a further piston-cylinder unit and a solenoid valve pressuremedium is supplied to the main cylinder. If necessary, that is to say ifin the brake circuit additional pressure medium is necessary orexpedient, this can be supplied from the further piston-cylinder unitand/or a travel simulator and/or a reservoir. In order to reduce thepressure for free travel control and/or fault cases pressure medium canbe discharged by a solenoid valve into the reservoir. This can beapplied for one or more brake circuits. Here via this connectionpressure can also be used from the reservoir to fill the brake circuits.This is useful if small main cylinders with lower volumes are used,which for example during fading require more volume.

According to the invention a method is also provided for operation of anactuating device of a motor vehicle brake system, wherein apiston-cylinder unit connected with at least one wheel brake is suppliedwith pressure medium. Here via a further piston-cylinder unit, adisplacement sensor and/or via a NO valve the piston-cylinder unit issupplied with pressure medium and by means of a booster disposed betweenthe piston-cylinder unit and the wheel brakes, the pressure supplied tothe wheel brakes is boosted.

If necessary, especially if the brake power boosting fails or forbraking with strong regeneration or ABS regulation with a low μ with lowpressure level in the wheel brakes, the volume metered into the brakecircuits can be supplied here from the further piston-cylinder unitand/or from the travel simulator. Here a volume stored in a storagecompartment can if required be supplied to the brake circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

With the help of the drawings, in the following description features andadvantages of the invention and its configurations are described in moredetail.

The drawings show as follows:

FIG. 1 system configuration of an actuating device according to theinvention of a motor vehicle brake system;

FIG. 2 an alternative arrangement of the further piston-cylinder unit orof the auxiliary piston;

FIG. 3 the pressure build-up with the use of the further piston-cylinderunit or the auxiliary piston in the event of failure of the brakebooster;

FIG. 4 pressure control of the solenoid valve;

FIG. 5 the arrangement of sensors used in the actuating device on asingle module;

FIGS. 6a-c the path of the push-rod piston travel and pedal tappet,pressure and brake booster boosting;

FIG. 7 another configuration of an actuating device according to theinvention.

DETAILED DESCRIPTION OF VARIOUS ASPECTS OF THE DISCLOSURE

FIG. 1 shows in a transparent manner the configuration of the systemwith the known basic components such as electric motor 1, rotor withspindle nut 1 a, spindle 2, push-rod piston 3, tandem main cylinder 4,return spring for push-rod piston 23, floating piston 21, 2× shutoffvalves 13, (storage compartment 24 with 2/2 solenoid valve 27 accordingto DE 10 2009 055721 with push-rod piston brake circuit 28), engineposition encoder 15 with redundant pedal travel sensors 11, brake pedal10 with pedal tappet 5. These components are for example described in DE10 2005 018649A1, reference to the full content of which is made herefor the sake of simplicity.

The brake pedal 10 operates by means of the pedal tappet 5 on theauxiliary piston 6, wherein the volume displaced by this via a line 45reaches the mechanical hydraulic travel simulator 8. With the movementof the auxiliary piston 6 the redundant pedal travel sensors 11 areconnected, controlling the engine and at the same time operating the NO2/2-pressure regulation solenoid valve 18, that is to say closing it.

The desired repercussion on the pedal force is generated by the travelsimulator 8. The auxiliary piston 6 is blocked in an intermediateposition with approximately 40% of the total piston travel S_(HK), ifthe travel simulator piston 8 a comes up against a stop. The solenoidvalve 18 has a pressure control function for safety reasons. As afunction of the travel simulator spring 8 b in the auxiliary piston 6 apedal travel-dependent pressure develops which corresponds to thepressure control function shown in FIG. 4. Should the travel simulatorpiston 8 a jam, then the pedal travel-pressure function is impaired,that is to say that via the solenoid valve 18 pressure medium flowsthrough the line 29 a to the reservoir 40.

With corresponding refinement of the response and switching behaviour,e.g. opening of the solenoid valve 18 with removal of pedal movementcontrol according to the solenoid valve 18, the feedback function of thetravel simulator 8 with piston and spring can be replaced, so that thesecan be dispensed with. In parallel with the solenoid valve 18 anon-return valve (not shown) for the reservoir may be necessary, inorder to avoid a depression during backwards movement of the auxiliarypiston.

The pressure control function is also used if the extreme pedal forcesdescribed operate. If a corresponding force is exceeded, then pressuremedium flows away and the auxiliary piston 6 moves once the travelS_(HK) comes up against a stop in the housing 41. Depending on theposition of the push-rod piston 3 and the coupled transmission tappet 5b the auxiliary piston 6 impinges on this and generates an additionalpressure in the tandem main cylinder 4, but which through itsdimensioning corresponds to the maximum required brake pressure, but notan excess pressure due to the high pedal forces. Thus for thedimensioning, weight and cost savings are possible. With thisoverstressing the motor and thus also the ABS/ESP function aredeactivated. The higher pressure operates exclusively on the auxiliarypiston 6 and travel simulator 8.

For a good response characteristic it is known to build in throttling ofthe operation as a function of the speed and direction. For this in theline to the travel simulator 8 a choke 19 is fitted and for rapid returna non-return valve 17. The auxiliary piston 6 is reset via return spring20. The auxiliary piston 6 with seals is guided and supported in asuitable housing 41. This housing 41 can be connected via a multi-partintermediate housing 42 in particular in plastic with the motor 1.Housing 41 and intermediate housing can also be one-piece.

At faster pedal speed through the choke 19 a higher pressure results.Accordingly the setting of the pressure control valve 18 untilactivation of the movement must be correspondingly higher.

In the event of failure of the brake booster the auxiliary piston 6 cancontinue to be used to optimise the braking effect. In the event offailure of the brake booster the pedal force should be as small aspossible, which calls for small main cylinder piston diameters. If theseare used, then in the low pressure range high pedal travels arenecessary due to the flat shape of the pressure-volume curve.

Via a NO 2/2-way solenoid valve, which is open if currentless, or feedvalve 30 (S_(E)) in the lower pressure range of the auxiliary piston 6pressure medium can be supplied for pressure build-up in the pistoncircuit 28. During pressure reduction via the pressure transducer 12pressure medium can be delivered back again to the auxiliary piston.

A further critical case is described in the introduction, if during ABSoperation on ice the brake booster fails and then a positive μ jumpduring braking occurs. In this case in the brake circuits a low pressurein the limiting case is 1-2 bar, so that the starting range of thepressure-volume curve at the actuation point of the travel simulatorbegins at approximately 40% pedal travel, which at the same timerepresents a piston travel and thus volume loss.

In systems in which the push-rod piston operates the travel simulator 8,then in this case the clearance to the floating piston iscorrespondingly small, with the result that, in this critical case, withsubsequent pressure build-up, only a very low pressure is possible inpush-rod piston circuit, which has a highly detrimental effect on thepossible braking effect. The abovementioned DE 10 2009 055721 describesa system for free travel control of the piston during ABS operation. Inorder that in the lower pressure range during ABS control push-rodpiston does not impinge on the pedal tappet, then a corresponding pistontravel and thus clearance to the pedal tappet=travel is achieved in thata corresponding volume is passed into a storage compartment 24. Theadvantage of this system in a critical case is that part of the volumecan be recovered in the brake circuit.

Instead of the storage compartment 24 with solenoid valve 27, forsimplification just a 2/2-way solenoid valve 27 a can be used, for freetravel control, that is to say when the clearance from the auxiliarypiston 6 or pole piece to the transmission tappet is too small. If thefree travel is excessive through corresponding piston control volume canbe sucked from the reservoir 40, so that this solenoid valve operates inboth directions.

This 2/2-way solenoid valve can also be used for the same function forone or more brake circuits, e.g. in the floating piston circuit, insteadof storage compartment 24 and upstream 2/2-way solenoid valve 27.

These valves can be used for an additional function of taking backvolume by corresponding piston control from the reservoir. This replacesthe supply compartment, for providing additional volume in the brakecircuit, if the main cylinder piston no longer achieves the necessarypressure. For this it is advantageous to design the main cylinder sealsto be stronger in order to be vacuum-tight. A switching device, e.g. asolenoid valve, can also be provided between the reservoir and the maincylinder. This is to prevent air being sucked into the brake circuitduring the above supply process. From the pressure and the pistonposition the volume is calculated which at the end of braking isdischarged into the reservoir again via the valve 27 a. This avoids themain cylinder seals being placed under excessive stress.

Both cases and solutions with storage compartment or valve 27 a can befurther improved if necessary, by using the volume of the auxiliarypiston in this critical case to improve the braking effect via the feedvalve S_(E) 30. The necessary feed and recovery of the auxiliary pistonis controlled via the pressure transducer.

An additional feed valve can also be used for further brake circuits,e.g. the floating piston circuit, in order in the limiting caseillustrated as the tailback solution to also supply volume from theauxiliary piston in the floating piston circuit, in order to achieve ahigher pressure level or a shorter pedal travel.

Reliable diagnosis of the valves 30 and 27 a, which open the brakecircuit(s) to the auxiliary piston 6 and to the reservoir, is ofessential importance. This can take place with the proposed diagnosticsprocedure once the door is opened by means of piston movement andpressure measurement.

Here the volume stored in the travel simulator 8 can also be used orisolated via a isolation valve 22,

With the potential of the auxiliary piston a decisive step towardsimproving failure safety is possible.

Of equal importance is the diagnosis of the functionally relevantcomponents. For this the system has two or at least one coupling. Thefirst frictional coupling 14 in particular embedded with a permanentmagnet 16 in a magnet housing 16 a, impinges on a pole piece 2 a of thespindle. This coupling is necessary on the one hand so that by means ofthe coupling force, especially at low pressures, the piston return viathe spindle is amplified.

The second coupling impinges on the front end of the transmission tappet5 b, which has a fixed connection via the magnet housing with thepush-rod piston 3. This frictional second coupling is in particularconfigured with a permanent magnet with pole 5 a on the auxiliarypiston. Between the pole 5 a and transmission tappet 5 b/26 a small freetravel is provided, which inter alia is used for the pedalcharacteristic and calibration of the pedal travel sensors.

For diagnosis of the auxiliary piston movement the spindle 2 withcoupling 26 is driven back, until with a free travel of 0 the fullcoupling force is effective. Here the push-rod piston in particular isup against the stop 43. With the subsequent forward movement theauxiliary piston can also be moved over the full stroke S_(HK) andmeasured via the pedal travel sensors 11. In the event of excessivefrictional force in the piston or inadequate coupling force the movementstops and the fault is detected. During this movement the valve 18 isopen. During a second movement the valve 18 is closed, the movement ofthe auxiliary piston is stopped via 17 and measured via sensor 11.

The diagnosis of the pressure control of the valve 8 is illustrated inFIG. 4.

The diagnosis of the feed valve S_(E) 30 with travel simulator 8 takesplace by pressure build-up via the spindle and piston with closedswitching valves 13. Here testing can take place via the pressuretransducer and the piston travel along with the feed valve 30 as well asthe travel simulator. For resetting the spindle the return spring 17 isplaced at the spindle exit and for structural reasons twice parallel tothe tandem main cylinder 4.

The storage compartment 24 with switching valves 13, 47 is shown hereonly in the push-rod piston circuit and described only for the functionof the two brake circuits in DE 10 2009 055721.

For the diagnosis described the state of the vehicle at a standstill isused, in particular after opening the door to enter the vehicle prior tostarting. In this case the vehicle may have been at a standstill for along period with all the conceivable influences affecting its functionsuch as corrosion, hardening of seals and so on.

The cases described with failure of the brake booster are based on afunctioning onboard vehicle electrical system. A total failure of theonboard vehicle electrical system during a journey is not assumed by theOEM. If nevertheless demands should be made of the additional functionsdescribed of the auxiliary piston and the switching of the solenoidvalve, then this can be resolved by a separate emergency circuit via anASIC with a small storage capacitor or auxiliary battery.

In FIG. 2 an alternative arrangement of the further piston-cylinder unitis shown. The auxiliary piston 6 is not concentric in this arrangement,but is disposed with an offset to the operational axis of the push-rodpiston 3. The transmission of the pedal force from the pedal 10 via thepedal tappet 5 and transmission element 5 c takes place via a gear unit.Here this has a triple joint design, for example.

The pivot joint operates as follows. The first connecting rod 6 c steersthe force into the articulated beam 6 d. This rotates about the axis ofrotation 6 b. In so doing the second connecting rod 6 a moves, which issupported by the piston 6. Thus the fluid in the master cylinder 1 isdisplaced via the line 20 into the travel simulator 8. This generates acounter-pressure. Thus at the pedal 10 a counter-force results, so thatthe pedal feel of a conventional braking system is simulated for thedriver. The rotation of the articulated beam 6 d can be assigned to adefined pedal position. Thus it is possible via, for example, a rotarysensor 11 to capture the pedal stroke. These two connecting rods 6 c and6 a are in particular designed in such a way that they are at a slightangle to the operational axis 2 and the axis of the piston 6. As aresult the transverse forces occurring when the brakes are operated arelow.

The transmission element 3 which is in particular designed as a spindleis driven by a brake booster 1, which is in particular designed as anelectric motor. This transfers an axial force to the piston 3, which ina main cylinder according to the art which is not shown delivers thebrake fluid into the brake circuit which is not shown.

In the fallback solution the solenoid valve 18 is opened. Thus if thepedal is moved the fluid is not displaced into the travel simulator 8but is able to flow without counter-pressure into the reservoir 40. Thusat the pedal no hydraulic loss of power of any note occurs. Accordinglythe entire pedal force can be transferred from the transmission element5 to the piston 3. In particular, between the transmission element 5 andthe piston 3 an operating tappet 5 b is disposed which engages via thetransmission element 3 and has a distance s from this. Thus the piston 3can also be operated if, for example, the transmission element 3 were tojam.

An advantage of disposing the master cylinder 1 with an offset to theoperational axis 2 is that the total installation length can be reduced.In vehicles with a short distance between the pedal 10 and the bulkheadthis is an advantage. Thus it is possible to bring the brake systemcloser to the brake pedal. As a result the installation spacerequirement in the engine compartment is reduced which has a positiveeffect, especially in the event of a crash.

FIG. 3 shows the course of the pressure or pedal force and the pedaltappet travel, Sp upon pressure build-up of the push-rod piston andauxiliary piston. Through switching at intervals, e.g. as a function ofpressure via the S_(E) valve, at time a, a considerably higher pressurelevel can be generated for the same pedal tappet travel S_(D), than withjust the push-rod piston and with considerably lower pedal forces thanwith the additional auxiliary piston. This means on the other hand thatthe flat part of the p-V characteristic curve does not require so muchpedal travel and with the subsequent steeper course of the p-Vcharacteristic curve the smaller push-rod piston can be switched to.

FIG. 4 shows the course of the pressure, pedal force and valve closingforce FM across the travel of the pedal tappet S_(P). In travelsimulator systems as a rule the course of the pedal travel force ismodelled, in particular in the lower pressure range. At higher pressuresthe characteristic curve is steeper, in order to save pedal travel,which in turn in the event of an emergency stop reduces the responsetime. The progression of the limiting current i is also shown, at whichthe current is known to have a quadratic effect on the magnetic force FMand thus the valve closing force. In the position S_(P1) it is nowassumed that the travel simulator piston clamps leading to an increasein pedal force and thus pressure. The switching limit FM₁ is exceeded,which then leads to further pedal movement, since the volume from theauxiliary piston passes through the valve until at S_(P2) the magneticforce FM₂ is again higher which in turn leads to a repeated pedalmovement. This assigned movement of the solenoid armature generates acurrent or voltage change, which in relation to the pedal tappetmovement SP can be evaluated for the purpose of diagnosis. Pressureregulation as a function of the speed of the brake pedal or connectedauxiliary piston has already been mentioned.

The actual current upon closing of the valve can also be determined forthe respective SP value. A braking process in particular with thevehicle at a standstill presents itself. Here the corresponding currentcan be reduced from the limiting value as a function of time until thepressure force on the valve is greater than the magnetic force. Here apedal tappet movement takes place which is measured and then immediatelythe current is raised again to the limiting value. If this response doesnot take place, then an error function is present so that then in arepeated test the brake booster can be deactivated.

In position S_(P2) the travel simulator is actuated. If now the highpedal force occurs, then at corresponding pressure the closing force ofthe valve is exceeded. The auxiliary piston moves under this highpressure as far as the stop in the housing.

FIG. 5 shows the combining of several sensors into a module. FIG. 1described how the system requires a position encoder for capturing therotor movement and thus the position of the piston and 2 (redundant)pedal travel sensors. These are disposed spatially in the pedalinterface. With a corresponding design of the pedal interface, it ispossible to combine these in a single module with a shared electricalconnection 39 (plug or multi-core cable) to the ECU.

The sensor component 33/33 a, e.g. Hall IC, is mounted on the printedcircuit board (PCB) 32. On the other side of the PCB 32 a rotor 35 ismounted in the housing 31. In the rotor the permanent magnet 34 isdisposed with corresponding polarity for activation of the sensor. Thesensor optionally delivers an analogue or digital signal. The rotor canbe moved by means of a toothed wheel 36, for example with the spindlenut, or a gear rack 37 connected with the auxiliary piston. The sensormodule is secured to the intermediate section of the housing anddisposed within a screening plate 38 or housing.

FIG. 6a shows the relationship between the push-rod piston travel S_(K)and the pedal tappet travel with and without brake booster. Once thebrake booster response value has been passed, essentially dependent uponthe pedal travel sensor, very quickly the movement S_(K) of the push-rodpiston occurs. With the brake booster this runs ahead of the pedaltappet. If the brake booster fails a free travel 1 takes place until thepedal tappet meets the push-rod piston and moves this.

FIG. 6b shows the course of the pressure with and without brake booster.After the response value of the brake booster a jump (so-called jumperfunction) in the pressure build-up occurs and then this proceeds as afunction of the travel simulator design. Without brake booster a freetravel is necessary until the push-rod piston closes the sniffer holeand then the pressure rises.

FIG. 6c shows the brake booster boosting as a function of the pedaltappet travel at the top at v>0 with travel simulator, thus in normaloperation. When the vehicle is at a standstill a switch is now possiblefrom travel simulator function at X to conventional follower amplifierfunction.

Here the pedal tappet impinges on the push-rod piston. Once the freetravel 1 has been passed the amplification is effective, so that therestoring forces of the piston and spindle are less perceptible andafter free travel 2 when the pressure builds up increases further. Herethe amplification can be selected in such a way that the same pedal feelresults as with the travel simulator, but without the stop.

Here the sequences have be shown if the vehicle is at a standstillduring braking.

For X₂ FIGS. 6a and 6c show when the vehicle is braked from v>0. Here inthe area between free travel 1 and 2 of the floating piston the value ofthe pedal tappet is used for control. If a certain pressure, e.g.braking at 10 bar to a standstill is maintained, then at this valuesimilarly the push-rod piston travel S_(K) will be brought into linewith the S_(PS) value.

FIG. 7 shows an actuating device 110 for a vehicle brake system. Theactuating device 110 has a tandem main cylinder 102, the pressurechambers 103, 104 of which are connected with an unpressurisedcompensation reservoir 105. In the housing 100 of the tandem maincylinder 102, supported by springs 107, 108, sealed axially displaceablecylinders 109, 110 are disposed. At one end of the tandem main cylinder102 a further piston-cylinder unit 111 is connected with the tandem maincylinder 102 or is integrated within this. This second piston-cylinderunit 111 can, for example for reasons of reduced installation length,also be disposed outside of the axis of the tandem main cylinder 102, asshown in DE 10 2010 045 617.9 from the same applicant, reference to thefull content of which is made here for the purposes of disclosure, or inthe form of a differential piston, which with an annular space formed bya partially expanded diameter of a partially reduced diameter forms asecond piston-cylinder unit, from which additional volume can besupplied, as is explained in DE 10 2009 031672 from the same applicant.In the cylinder part 112 of this second piston-cylinder unit 111 anaxially displaceable piston 113 is disposed, having an extension 114,which penetrates in a sealed manner an opening 115 in an intermediatewall 116 and rests on the piston 110, in order to impinge on this.

An actuating device 117 in the form of a brake pedal 118 is connectedwith the piston 113 via a rod assembly 122.

From the pressure chamber 112 a formed by the cylinder of the secondpiston-cylinder unit 111 a hydraulic line 125, in which a NO 2/2-wayvalve 126 is connected, leads via an annular groove 127 formed in thetandem main cylinder 102 to the compensation reservoir. From thishydraulic line 125 a further hydraulic line 128 branches off, in which anon-return valve 129 is arranged and which leads to the pressure chamberof the tandem main cylinder. Alternatively a NC solenoid valve 142 canalso be used.

This alternative has the advantage that both the volume supply from theadditional piston-cylinder unit 111 in terms of pressure level and thepressure reduction are controlled via the pressure transducer 133. Inthis case the volume reaches the reservoir via the line 128 and thesolenoid valve 126.

From the hydraulic line 128 a hydraulic line 129 branches off, which viaa NC 2/2-way valve 130 leads to a hydraulic travel simulator 131.

In the hydraulic line 132 a pressure or pressure transducer 133 isdisposed. A hydraulic line leads from the line 128 to a unit (HCU) 135,which can contain valves in configurations not shown in more detail, inorder to control or regulate the pressure in the (similarly not shown)wheel brakes.

The HCU also contains an amplifier, which has at least a pressuregenerator, such as for example an electric motor and pump withcorresponding control elements and thus forms an electro-hydraulic brakeunit (EHB).

The method of operation of the configuration shown in FIG. 7 isexplained in the following:

Upon operation of the actuating device or the brake pedal 118 the piston113 in FIG. 7 is displaced to the left and in doing so forces thehydraulic medium through the line 128 and the open valve 126 into thecompensation reservoir. At the same time, via the extension 114 thepush-rod piston 109 is moved to the left. The resultant pressure in thepressure chamber 103, when the 2/2-way valve 130 is open can impingewith pressure upon the piston of the travel simulator working againstthe spring pressure. In other words with this construction the travelsimulator 131 is controlled by the pressure in the push-rodpiston-circuit and can be deactivated via the 2/2-way valve. Here thepressure built up is measured by the pressure transducer and themeasured values passed to an evaluation unit (ECU) which is not shown.The pressure desired by the driver or the resultant braking effect isdetermined by a travel sensor 119 on the brake pedal, the measuredvalues of which are passed to the ECU and compared with the values ofthe pressure transducer. Here the functionality of the travel simulator131 can be achieved here by means of a device with two elements arrangedbetween brake pedal 118 and piston 113 and movable in relation to oneanother and, supported against one another by an elastic member, therelative movement of which is measured by two displacement sensors (ofwhich only one is shown here) and evaluated by the ECU. Alternativelyalso the signal from the displacement sensor 119 can be compared withthe signal from pressure transducer 133 and in the event of animplausible correlation the brake booster function deactivated and thissignal given out as a warning indicator.

In the event that the amplifier fails (fallback solution), the 2/2-wayvalve 126 can be closed, so that the volume displaced by the piston 109or 113 is used in full for pressure generation, wherein the hydraulicvolume displaced in the further piston-cylinder unit 111 can be providedto the brake circuits as additional volume. Here control of the solenoidvalve 126 can take place via the pressure transducer 133, so that forexample the feeding of hydraulic medium into the brake circuit onlytakes place at up to around 20 bar. The control of the pressurereduction can also take place via this solenoid valve, as alreadymentioned.

The piston-cylinder unit can also be represented by two units parallelto the axis, e.g. outside of the tandem main cylinder, which has anadvantageous effect on the installation length.

According to a further aspect of this disclosure, a redundant solenoidvalve power supply may be provided, which may be used in case of totalfailure of the vehicle's onboard electrical system.

LIST OF REFERENCES

-   1 Electric motor-   1 a Rotor with spindle nut-   2 Spindle-   2 a Pole piece of the spindle-   3 Push-rod piston-   4 Tandem main brake cylinder-   5 Pedal tappet-   5 a Pole at auxiliary piston-   5 b Transmission tappet-   5 c Transmission element-   6 Auxiliary piston-   6 a First connecting rod-   6 b Axis of rotation of articulated beam-   6 c Second connecting rod-   6 d Articulated beam-   7 Free travel (s) at pedal tappet-   8 Travel simulator or travel simulator housing-   8 a Travel simulator piston-   8 b Travel simulator spring-   10 Brake pedal or actuating device-   11 Pedal travel sensor-   12 Pressure transducer-   13 Switching valve-   14 First coupling-   15 Position encoder-   16 Permanent magnet-   16 a Magnet housing-   17 Spindle return spring-   18 Pressure regulation solenoid valve S_(D)-   17 Non-return valve-   19 Choke-   20 Return spring for auxiliary piston-   21 Floating piston-   22 Isolation valve for travel simulator-   23 Return spring for push-rod piston-   24 Storage compartment-   26 Second coupling-   27 2/2-way solenoid valve for storage compartment-   27 a 2/2-way solenoid valve for free travel control-   28 Brake circuit push-rod piston-   29 Line to travel simulator-   29 a Line to reservoir-   30 Feed valve S_(E) or 2/2-way valve-   31 Sensor housing-   32 PCB or film-   33 Sensor component of rotation angle sensor-   33 a Sensor component of pedal travel sensor-   34 Magnet-   35 Rotor-   36 Toothed wheel-   37 Gear rack-   38 Screening plate-   39 Electrical connection-   40 Reservoir-   41 Housing for auxiliary piston-   42 Housing intermediate part-   43 Push-rod piston stop-   45 Line-   101 Actuating device-   102 Piston-cylinder unit or tandem main cylinder-   103 Pressure chamber-   104 Pressure chamber-   105 Compensation reservoir-   106 Housing-   107 Spring-   108 Spring-   109 Piston (push-rod piston)-   110 Piston (floating piston)-   111 Piston-cylinder unit-   112 Cylinder part-   112 a Pressure chamber-   113 Piston-   114 Extension-   115 Opening-   116 Intermediate wall-   117 Actuating device-   118 Brake pedal-   119 Pedal travel sensor-   122 Rod assembly-   125 Hydraulic line-   126 2/2-way valve-   127 Annular groove-   128 Hydraulic line-   129 Non-return valve-   130 2/2-way valve-   131 Travel simulator-   132 Hydraulic line-   133 Pressure sensor or pressure transducer-   135 HCU-   142 Solenoid valve

What is claimed is:
 1. A method for diagnosing a brake system of avehicle, including: closing at least one switching valve located on afirst hydraulic line between a first piston-cylinder unit and at leastone wheel brake; closing a feed valve located on a second hydraulic linebetween an auxiliary piston-cylinder unit and the at least one wheelbrake; using an electro-mechanical drive device to drive a piston of thefirst piston-cylinder unit to provide a pressure; and diagnosing thefeed valve by measuring the pressure.
 2. The method according to claim1, further comprising discharging volume into a reservoir for pressurereduction for free travel control and/or in case of fault.
 3. The methodaccording to claim 1 further including adaptively controlling a brakebooster, wherein the adaptive controlling of the brake booster isswitched to a follower amplifier function when the vehicle is at astandstill.
 4. The method according to claim 1, further comprisingsupplying volume into brake circuits from the auxiliary piston-cylinderunit and/or from a travel simulator if brake boosting fails at low μ. 5.The method according to claim 1, further including supplying a volumestored in a storage compartment to brake circuits as necessary.
 6. Themethod according to claim 1, further comprising using a motor current ofthe drive device and/or a pressure transducer for diagnosis.
 7. Themethod according to claim 1, wherein the method is performed to test atravel simulator.
 8. The method according to claim 1, wherein the methodis performed when the vehicle is at a standstill.
 9. The methodaccording to claim 1, wherein the method is performed when the vehicleis at a standstill and a door is opened before a start.
 10. The methodaccording to claim 1, wherein the pressure is built up over a valve thatis open if currentless.
 11. The method according to claim 1, furthercomprising using the electro-mechanical drive device to drive a pistonof the first piston-cylinder unit to provide the pressure in a brakecircuit, wherein the pressure in the brake circuit is measured.
 12. Anactuating device for a vehicle brake system, comprising: anelectro-mechanical drive device configured to drive a piston of a firstpiston-cylinder unit; at least one wheel brake, that is connected via atleast one switching valve and at least one hydraulic line with the firstpiston-cylinder unit; an auxiliary piston-cylinder unit, comprising apiston operated using a pedal; and a travel simulator configured toreceive pressure medium from the auxiliary piston-cylinder unit, whereinpressure medium from the auxiliary piston-cylinder unit is able to besupplied to the at least one wheel brake via a brake circuit feed valve;and wherein the actuating device is arranged so that the feed valve andthe travel simulator are able to be tested by closing the feed valve andthe at least one switching valve and by providing a pressure by theelectro-mechanical drive device to the first piston-cylinder unit andmeasuring the pressure.